Lewandowski has been a star for Dortmund this season, scoring 14 goals in the Bundesliga and guiding his side to the top of the table.
His performances have seen him linked with a move away from the Signal Iduna Park recently, and his agent Cezary Kucharski, has refused to rule out a possible exit, although he insists the player is only interested in moving to one of Europe's top sides.
"We are only interested in the top clubs, such as Chelsea or Manchester United," Kucharski told Przeglad Sportowy.
"In addition, I am working on other options in Germany, England and possibly Spain. Robert would prove himself in any team in the world."
The agent also refused to rule out a potential move to Dortmund's Bundesliga rivals Bayern Munich.
"Borussia are seen as a good club but, in terms of popularity, they will never match Bayern.
"It's as if one would compare Slask Wrocaw in Poland with Legia Warsaw. Slask can be leaders of the league, but most people will still always talk about Legia."
Kucharski also believes Dortmund would not be able to keep hold of Lewandowski if a significant offer came in, and is hoping the player will enhance his reputation with a strong showing at this summer's European Championships.
"It is true that Dortmund have again repeated that Robert is not for sale, but in the end it is all a question of price.
"Currently Robert is worth between €15 and €20million. But I hope that the European Championships will be a great success [for him]."
Dortmund are next in action on Saturday when they take on Bayer Leverkusen at the Signal Iduna Park.